Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting a reception acknowledgement for a hybrid automatic repeat request (HARQ) in a wireless communication system in which serving cells using a radio frame of different types with each other are aggregated.
Related Art
Long Term Evolution (LTE) based on 3rd Generation Partnership Project (3GPP) Technical Specification (TS) Release 8 is the leading next-generation mobile communication standard.
As disclosed in 3GPP TS 36.211 V8.7.0 (2009-05) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, in LTE, a physical channel can be divided into a Physical Downlink Shared Channel (PDSCH) and a Physical Downlink Control Channel (PDCCH), that is, downlink channels, and a Physical Uplink Shared Channel (PUSCH) and a Physical Uplink Control Channel (PUSCH), that is, uplink channels.
A PUCCH is an uplink control channel used to send uplink control information, such as a Hybrid Automatic Repeat reQuest (HARQ), an acknowledgement/not-acknowledgement (ACK/NACK) signal, a Channel Quality Indicator (CQI), and a Scheduling Request (SR).
Meanwhile, 3GPP LTE-Advanced (A) that is the evolution of 3GPP LTE is in progress. Technology introduced into 3GPP LTE-A includes a carrier aggregation.
A carrier aggregation uses a plurality of component carriers. A component carrier is defined by the center frequency and a bandwidth. One downlink component carrier or a pair of an uplink component carrier and a downlink component carrier correspond to one cell. It can be said that a terminal being served using a plurality of downlink component carriers is being served from a plurality of serving cells.
A time division duplex (TDD) system uses the same frequency in downlink and uplink cases. Therefore, one or more downlink subframes are associated with an uplink subframe. The ‘association’ implies that transmission/reception in the downlink subframe is associated with transmission/reception in the uplink subframe. For example, when a transmission block is received in a plurality of downlink subframes, a user equipment transmits HARQ ACK/NACK (hereinafter, ACK/NACK) for the transmission block in the uplink subframe associated with the plurality of downlink subframes. At the moment, a minimum time is required to transmit the ACK/NACK. This is because a time for processing the transmission block and a time for generating ACK/NACK are required.
A frequency division duplex (FDD) system uses different frequencies in downlink and uplink cases. The uplink subframe and the downlink subframe have the relationship of 1:1. In this case, the ACK/NACK for the transmission block which is received in the downlink subframe is transmitted in the uplink subframe after four subframes.
Meanwhile, in a next generation wireless communication system, a serving cell that uses the TDD and a serving cell that uses the FDD may be aggregated. That is, a plurality of serving cells that use a radio frame of different types with each other may be allocated to a user equipment. In this case, it is problematic in which way the ACK/NACK is transmitted.